Cell growth behaviors of Clostridium acetobutylicum in a pervaporation membrane bioreactor for butanol fermentation.

Acetone-butanol-ethanol fermentation using Clostridium acetobutylicum was studied in the continuous and closed-circulating fermentation (CCCF) system. The experiment lasting for 192 H was carried out by integrating fermentation with in situ pervaporation. In the entire process, the cell growth profile took place in the following two phases: the logarithmic phase during early 28 H and the linear phase from 130 to 150 H. This was a unique characteristic compared with the curve of traditional fermentation, and the fitting equations of two growth phases were obtained by Origin software according to the kinetic model of cell growth. Besides, the kinetic parameters that include the butanol yield, maximum specific growth rate, average specific formation rate, and volumetric productivity of butanol were measured as 0.19 g g(-1) , 0.345 H(-1) , 0.134 H(-1) and 0.23 g L(-1)  H(-1) , respectively. The C. acetobutylicum in the CCCF system showed good adaptability and fermentation performance, and the prolonged fermentation period and high production were also the main advantages of CCCF technology.

Combination of in situ preconcentration and on-site analysis for phosphate monitoring in fresh waters.

Excess nutrients of phosphorus and nitrogen would lead to adverse impacts on a water body. It is important that their concentrations in a dynamic water ecosystem are measured accurately and constantly for an early warning before occurrences of algal blooms and for environmental management. Nevertheless, on-site measurements by existing technologies are often limited by the inherent sensitivities. In this study, a portable system for dissolved phosphate monitoring in freshwater based on the diffusive gradients in thin films (DGT) technique was developed. A polydiallydimethylammonium chloride (PDA) aqueous solution and a dialysis membrane were used as a binding phase and a diffusive layer in this preconcentration device, respectively. The binding properties of the PDA solution were evaluated in solutions of different pH (3 to 9) and varying concentrations of anions (2.0-20 mM). The amount of phosphates preconcentrated in the devices was measured by ultraviolet-visible (UV) spectroscopy to obtain the concentrations in waters without elution steps. The devices were validated in synthetic river water with good agreement with the theoretical prediction and in natural river water. A system combining this preconcentration device and a compact detection chamber equipped with a pair of light emitting diodes (LED) was studied in lab synthetic solutions for on-site monitoring of phosphate concentrations and their fluctuations.

Measurement of stable and radioactive cesium in natural waters by the diffusive gradients in thin films technique with new selective binding phases.

A cesium-specific diffusive gradients in thin films (DGT) technique was developed using copper ferrocyanide (CFCN) as the binding agent. Two types of DGT binding phases were evaluated, one by immobilizing CFCN on Chelex 100 resin gels (Chelex-CFCN) and the other on poly(acrylic acid) gels (PAA-CFCN). Both DGT devices were successfully applied to the measurement of low levels of stable 133Cs and radioactive 137Cs in synthetic solutions and in natural river waters. In all cases, the DGT labile concentrations measured with the PAA-CFCN DGT agreed very well with total dissolved Cs concentrations, whereas those measured by the Chelex-CFCN DGT were much lower than total Cs concentrations. The difference was attributed to the different binding kinetics of Cs+ on the two gels suggesting that this might be a promising means of measuring biologically relevant Cs concentrations in natural waters.

Inhibition effect of secondary metabolites accumulated in a pervaporation membrane bioreactor on ethanol fermentation of Saccharomyces cerevisiae.

The secondary metabolites accumulated in a pervaporation membrane bioreactor during ethanol fermentation were mostly composed of acetic acid, lactic acid, propionic acid, citric acid, succinic acid and glycerol. The inhibition effect of these compounds at a broad concentration range was studied through ethanol fermentation by Saccharomyces cerevisiae. An increasing concentration of the secondary metabolites led to longer lag time and a reduction of cell growth. The specific cell growth rate, cell yield, ethanol productivity were only 0.061 h(-1), 0.024, 0.47 g L(-1) h(-1) respectively, when the medium contained 3.12 g of acetic acid, 10.23 g of lactic acid, 2.72 g of propionic acid, 1.35 g of citric acid, 2.26 g of succinic acid and 49.25 g of glycerol per liter (a concentration level in pervaporation membrane bioreactor at later fermentation period). By increasing pH of the medium to 6.0-8.0, the inhibition of these secondary metabolites could be greatly relieved.

Enhanced ethanol fermentation in a pervaporation membrane bioreactor with the convenient permeate vapor recovery.

A continuous and closed-circulating fermentation (CCCF) system with a pervaporation membrane bioreactor was built for ethanol fermentation without a refrigeration unit to condense the permeate vapor. Two runs of experiment with a feature of complete and continuous coupling of fermentation and pervaporation were carried out, lasting for 192h and 264h, respectively. The experimental measurement indicated that the enhanced fermentation could be achieved with additional advantages of convenient permeate recovery and energy saving of the process. During the second experiment, the average cell concentration, glucose consumption rate, ethanol productivity, ethanol yield and total ethanol amount produced reached 19.8gL(-1), 6.06gL(-1)h(-1), 2.31gL(-1)h(-1), 0.38, and 609.8gL(-1), respectively. During the continuous fermentation process, ethanol removal in situ promoted the cell second growth obviously, but the accumulation of the secondary metabolites in the broth became the main inhibitor against the cell growth and fermentation.

Acetone-butanol-ethanol fermentation in a continuous and closed-circulating fermentation system with PDMS membrane bioreactor.

Acetone-butanol-ethanol (ABE) fermentation by combining a PDMS membrane bioreactor and Clostridium acetobutylicum was studied, and a long continuous and closed-circulating fermentation (CCCF) system has been achieved. Two cycles of experiment were conducted, lasting for 274 h and 300 h, respectively. The operation mode of the first cycle was of fermentation intermittent coupling with pervaporation, and the second cycle was of continuous coupling. The average cell weight, glucose consumption rate, butanol productivity and butanol production of the first cycle were 1.59 g L(-1), 0.63 g L(-1)h(-1), 0.105 g L(-1)h(-1) and 28.03 g L(-1), respectively. Correspondingly, the four parameters of the second cycle were 1.68 g L(-1), 1.12 g L(-1)h(-1), 0.205 g L(-1)h(-1) and 61.43 g L(-1), respectively. The results indicate the fermentation behaviors under continuous coupling mode were superior to that under intermittent coupling mode. Besides, two peak values were observed in the time course profiles, which means the microorganism could adapt the long CCCF membrane bioreactor system.

Sodium polyacrylate as a binding agent in diffusive gradients in thin-films technique for the measurement of Cu2+ and Cd2+ in waters.

An aqueous solution containing sodium polyacrylate (PA, 0.0030M) was used in diffusive gradients in thin-films technique (DGT) to measure DGT-labile Cu(2+) and Cd(2+) concentrations. The DGT devices (PA DGT) were validated in four types of solutions, including synthetic river waters containing metal ions with or without complexing EDTA, natural river water (Hun River, Shenyang, China) spiked with Cu(2+) and Cd(2+), and an industrial wastewater (Shenyang, China). Results showed that only free metal ions were measured by PA DGT, recovery=98.79% for Cu(2+) and recovery=97.80% for Cd(2+) in solutions containing only free metal ions, recovery=51.02% for Cu(2+) and recovery=51.92% for Cd(2+) in solution with metal/EDTA molar ratio of 2:1 and recovery=0 in solutions with metal/EDTA molar ratio of 1:1 and 1:2. These indicated that the complexes of Cu-EDTA and Cd-EDTA were DGT-inert or not DGT-labile. The DGT performance in spiked river water (recovery=8.47% for Cu(2+) and recovery=27.48% for Cd(2+)) and in industrial wastewater (recovery=14.16% for Cd(2+)) were also investigated. Conditional stability constants (logK) of PA-Cu and PA-Cd complexes were determined as 6.98 and 5.61, respectively, indicating strong interaction between PA and the metals.